Mine is also a maxed out iMac 5k with Sierra. Got it working. My main archive is a huuuuge C1 Catalog. When applying profiles to a picture C1 is giving me the beachball.
If I create a fresh session/catalog - everything is OK
Anyone getting these to work with the new Capture One Pro v10 ?
My mac running the new C1 v10 is giving me the beachball when I select any of the custom X-T1 profiles